Magnetic separation is a method of separating materials which have different magnetic properties. This method is applied by means of a separator. The magnetic separators which are used in the ore preprocessing industry, above all in the case of ferromagnetic materials, are mostly magnetic drum separators. Drum separators exist in various forms of embodiment, e.g. drum separators which operate with the flow and against the flow. The drum separator separates out a material to be processed into a stream of useful materials and a stream of waste materials. In other words, using such separation processes, useful materials are to be separated from non-useful ones, as a stream of useful materials and a waste material stream. In particular in mining, weak-field drum separators are used for magnetite enrichment. This method or process, as applicable, can be realized using a constant or alternating magnetic field. For example, in the preparation of magnetite ores, permanent magnets are mostly used.
The drum of the drum separator is not itself magnetic. Within the drum there is a system of magnets which consists of permanent magnets or electromagnets. The drum represents the part of the separator which, in operation, is movable, namely rotates about its axis of rotation, and the position of the axis is fixed in space or location, as applicable. On the other hand, the system of magnets forms a part which is essentially unmovable.
The pipe material, as the material to be processed, is introduced into the separator in an upper or lower region of the rotating drum. In this case, for wet separation the material to be processed is deposited as a suspension, also called a slurry. The magnetic poles of the separator are distributed around the circumference of the drum, with defined spacings, or a defined geometry, as applicable. The geometric arrangement of the magnets determines the field geometry in the separation zone. The so-called gap size, that is the distance between the system of magnets and the material to be processed or the drum, as applicable, determines how the separator works, and has a decisive influence on the output streams emerging from the drum separator, namely the stream of waste materials and the stream of useful material. If the gap is too small, too much material will be attracted by the magnetic attractive force from the system of magnets, so that even grains with only a low ferro-magnetic content are attracted onto the drum wall, and pass into the stream of useful material. The selectivity of the separator is thereby limited, and the quality of the stream of useful material is then too low. On the other hand, if the gap is too large only very strongly magnetized particles will be carried along with the stream of useful material because of a high ferro-magnetic content in the particles, so that the throughput of the separator is limited. Useful material, i.e. for example magnetic material, then also passes into the stream of waste materials, which reduces the yield of useful material. In both cases, the specific energy consumption of the drum separator rises, in the first case mentioned above it rises additionally because more waste materials, e.g. low grade ore, are present in the stream of useful material and thus, for example, will be transported into a subsequent milling stage.
In a magnetic separator for ore preparation, it is not only the number of magnets but also the distance between the magnets which is an important constructional characteristic. The intent is to use the magnets and their spacing from each other, by repeated changing or by interruption of the magnetic field strength, and thus by changing the magnetic force on the iron particles toward the drum, to prevent the formation of agglomerations during the separation process along the direction of flow of the material to be separated, i.e. the sticking together or concretion of iron-containing rock and gangue in the slurry. As a geometric characteristic, the spacing of the magnets from one another combined with the above spacing gap between the system of magnets and the drum wall is thus adjusted for the relevant composition of the ore, the grain size or the particle distribution in the slurry, as applicable, the solid matter content in the slurry, and hence for the composition of the slurry. The separator concerned can thus only be optimally used for the particular conditions specified.
These facts result in the separator losing efficiency when there are changes in the properties of the material to be processed, e.g. the ore, and thus after a certain operating period no longer being optimally adjusted for the product quality, or the yield, which is to be achieved in the output streams. The magnetic separator does not react to changed properties in the input material, that is the material to be processed. Here, changed properties might for example be a changed ratio of magnetic ores to non-magnetic rock.
Specifically, the composition of the ore comprising the material to be processed may change due to inhomogeneities in the rock, or in the mineral composition of the area being mined. As a consequence the separation process, and thus the machine parameters for the magnetic drum separator, must be adapted in order to ensure a constant high-quality or improved quality from the separation process.
The usual forms of construction of drum separators use mainly systems of magnets with permanent magnets. The system of magnets in the drum separator is laid out and installed according to the particular separation task concerned, and the system of magnets is consequently permanently built into the magnetic drum separator. If there is a change in the composition of the ore comprising the material to be processed, a constructional change must be made to the magnetic drum separator. This is carried out with the drum separator shut down. No other form of change is possible. The separator is thus adjusted for a particular ore sample. A change in the composition of the ore or the grain size of the ore necessitates the shutting down of the separator and conversion measures on the set of magnets, that is the arrangement of the magnets.
Changes of this sort to the constructional layout cannot at present be carried out during ongoing operation of the drum separator. It must be halted, i.e. an operational shutdown must be carried out. A machine operator then makes the appropriate changes to the drum separator or system of magnets, as applicable. An adaptation of this sort to the magnetic drum separator is also described, in the sense that it is a manual regulatory action, as so-called open-loop regulation by the machine operator. Adaptations which are necessary are in this case initially recognized by the operator, and are then carried out on the machine by means of constructional modification actions while machine operations are shut down, e.g. the set of permanent magnets is modified.
A drum separator is known from U.S. Pat. No. 7,841,474 B2 in which a system of magnets in roller form lies against the inner wall of the rotating drum. The contact pressure of the magnetic roller together with the site of its contact on the drum can be adjusted by a change in the position of the magnetic roller with the machine shut down.
From RU 222 0775 C1 and RU 23 75 117 C1, drum separators are known in which each of the magnets of the magnet set can rotate about an axis which runs through the magnet concerned. In other words, the orientation of the magnetic field of an individual magnet, together with the strength and the profile of the resulting overall magnetic field, can be altered. The axes of rotation run parallel to the axis of rotation of the drum.
WO 1998 019 795 A1 discloses how to rotate magnetic rollers also about an axis which passes through them. Here again, the axis runs parallel to the axis of rotation of the drum.
From RU 238 01 64 C1, it is known how to change the angle of inclination of individual permanent magnets relative to one another. Here again, the magnets rotate about axes of rotation which run through themselves, or in their immediate neighborhood.
Also known is how the position of the system of magnets in the drum can be manually relocated—with the machine shut down—in the sense that it can be rotated in its entirety about the axis of rotation of the drum. In so doing, the distance between the system of magnets and the drum is not changed. In other words, in the interior of the drum the air gap between the system of magnets and the non-magnetic drum is constant, and with the available solutions it cannot be changed. Because the material which is to be separated, i.e. the material being processed, is located on the outer perimeter of the drum, the distance from the system of magnets to the material to be separated is thus also constant and can also not be changed.
US 2011163015 A1 discloses a magnetic drum separator with a drum which can rotate about the axis of rotation and with an arrangement of magnets, having a plurality of magnets, arranged in the interior space of the drum. The individual magnets are arranged on a plate, which can pivot so that the position of the magnets relative to the axis of rotation of the drum separator can be altered.
U.S. Pat. No. 1,729,008 A discloses a magnetic drum separator which has a rotatable drum with an arrangement of magnets incorporating electromagnets. The position of the electro-magnets can be altered relative to the axis of rotation of the drum.
U.S. Pat. No. 2,785,801 A specifies a magnetic drum separator which has, arranged on a frame, magnets the position of which relative to the axis of rotation of the drum separator can be altered by means of the frame, even while the drum separator is in operation.